Fluoropolymers such as polytetrafluoroethylene ("PTFE") and hexafluoropropylene-tetrafluoroethylene copolymers ("HFP-TFE") have a number of desirable properties for a number of applications. For example, in general they have high thermal stability, high chemical inertness, low frictional properties, high electrical resistance, high solvent resistance and high impermeability to liquids and gases.
Over the years considerable efforts have been expended in devising ways of modifying these polymers in order to render them more suitable for particular end uses. Typical of such efforts are the following:
U.S. Pat. No. 2,710,290 to Safford et al. describes mixtures of an organopolysiloxane of the type that is convertible by heat to the cured, solid elastic state and a minor proportion--preferably less than 25% by weight--of fibers of solid PTFE randomly dispersed in the organopolysiloxane. The patent also describes the cured or vulcanized products formed from mixtures of these two components together with a curing agent such as benzoyl peroxide and fillers such as silica aerogel or diatomaceous earth.
U.S. Pat. No. 2,934,515 to Konkle et al. describes PTFE-silicone compositions suitable for use in forming gaskets. These compositions are formed by milling an organopolysiloxane gum with dry particles of solid PTFE whereby the shearing action of the mill causes the PTFE particles to deform and elongate, forming fibers in the gum. The milled mixture is then vulcanized, preferably by heating the milled mixture with an organic peroxide. Reference is made in the patent to use of 20 to 80 parts by weight of the organopolysiloxane gum per 100 parts by weight of the PTFE.
U.S. Pat. No. 2,940,947 to Welch et al. points out that prior attempts to soften fluorine-containing polymers had been unsuccessful because of the incompatibility of conventional softeners such as silicone oils with the fluoropolymers. In circumventing this problem the patentees found it possible to increase the tensile strength and decrease the hardness of the fluoropolymers by incorporating the softener or plasticizer such as silicone oil into fluoropolymers in the presence of a finely-divided, hydrated siliceous pigment having an average ultimate particle size below 0.1 micron.
U.S. Pat. No. 2,907,795 to Wolfe describes certain fluorine-containing co-telomers which are high boiling liquids indicated to be specially useful as lubricants at extreme ranges of temperature.
U.S. Pat. No. 3,103,490 to Green describes wax-like fluorocarbon telomer compositions comprising a fluorocarbon telomer and an ester of orthotitanic acid. The compositions are indicated to have improved abrasion resistance, desirable lubricating properties and improved adhesion to the surface of materials to which they are applied.
U.S. Pat. No. 3,223,739 to Teumac refers to pyrolytic degradation of PTFE as a way of producing fluorocarbon waxes. It is stated that such pyrolysis usually produces 60% yields of waxes, the remainder being low boiling fluorocarbons and a small amount of carbon, which can be a highly activated form of carbon.
U.S. Pat. No. 5,077,362 to Watanabe et al. describes vinylidene fluoride copolymers comprising as monomer units at least 50 mol % of vinylidene fluoride and at least 0.1 mol % of an organosilicon compound containing at least one silicon-bonded vinyl group and at least one acryloyloxy or methacryloyloxy or vinyloxy group in the molecule. It is indicated that the copolymers can be dissolved in fluorine-containing solvents such as trichlorotrifluoroethane and hydrocarbon solvents such as cyclohexane to form solutions useful for producing thin films or coatings having good weather and chemical resistance.
U.S. Pat. No. 5,256,745 to Groothaert refers to preparing fluorine-containing polymers by conducting the polymerization of a fluorine-containing ethylenically unsaturated monomer, e.g., tetrafluoroethylene, under free-radical conditions in a mixture which contains a non-free radically polymerizable organometallic comprising a group IV metal atom, e.g., Si, and an aliphatic carbon atom bonded directly to that metal atom and to a hydrogen atom, e.g., a tetraalkylsilane, tetraalkylstannane, or tetraalkylgermane. The resultant polymers are indicated to have a saturated carbon-to-carbon backbone chain whose interpolymerized units are derived from the ethylenically unsaturated monomers, and at least one organometallic group derived from the organometallic compound, which organometallic group preferably terminates a polymer chain or branch as an end group. The polymers can be compounded and cured.